A CELLULAR LIGAND-FIELD MODEL FOR L-L SPECTRAL INTENSITIES .4. PLANAR AND NEAR-PLANAR TETRACHLOROCOPPER(II) IONS

The intensity distributions in the 'd-d' spectra of three planar CuCl42- chromophores are reproduced quantitatively within the theoretical model described in the preceding paper. Intensity for these species, namely bis(1-methyl-4-oxo-3,3-diphenylhexyldimethylammonium)tetrachlorocopper(II), bis(2-imino-1-methyl-4-imidazolidinium)tetrachlorocopper(II) and bis(N-methylphenyl-ethylammonium)-tetrachlorocopper(II), is deemed to arise dynamically via the bending vibrations. Fair reproduction of experimental absorbances is achieved using the b2u mode alone, this being known to be the softest vibration in these systems. The roles of spin-orbit coupling and small departures from D4h symmetry are discussed. Nearly perfect reproduction of experiment is obtained with addition of small contributions from the e(u) bend. The intensity distribution in the 'd-d' spectrum of the pseudo-tetrahedral chromophore, bis(N-benzylpiper-azinium)tetrachlorocopper(II), is reproduced quantitatively within the 'static' model described in part I of this series. Comparisons between the parameter values obtained from the 'static' analysis with those from the 'dynamic' analysis for the planar chromophores suggest that dynamic modelling with both b2u and e(u) modes is the more physically persuasive. The efficacy of the model in part IV is critically reviewed in this first application.